He also had criticized former daughter-in-law Christine Belford of Pike Creek, Del., whom he fatally shot in the courthouse lobby along with Belford's friend and neighbor Laura Elizabeth "Beth" Mulford, as an irresponsible mother. The family had hired a private investigator to follow her, he said in 2009.

"We've gone through hell and beyond with this," Thomas F. Matusiewicz said then. "It's a damn shame. We want to make sure our granddaughters are safe. It's not acceptable."

Belford and former Newark, Del., optometrist David Matusiewicz had battled for custody after their 2006 divorce. The younger Matusiewicz absconded with his daughters and his mother, living in Panama, Costa Rica, Mexico and Nicaragua for 18 months as they evaded an international manhunt.

He had told the girls that their mother had committed suicide, according to reports. They were found living in a trailer in the Nicaraguan village of Catalina, where they called themselves the Blanco family.

David Matusiewicz, 45, was released last year from federal prison in Bastrop, Texas, after being convicted in Delaware federal court of kidnapping and bank fraud for forging Belford's name to get a $249,000 home equity loan.

David Matusiewicz was at the courthouse Monday for a child support hearing involving his ex-wife and their three daughters, ages 7, 10 and 11, law-enforcement sources said.

After the shooting, David Matusiewicz was found inside the courthouse and was taken into custody. He was being questioned Monday night.

Belford, who had worked as a contact lens technician, said in December that she and David Matusiewicz, whose parental rights had been terminated, still were battling in court about overdue child support.

"Kids are doing OK," she wrote to The News Journal. "Some lingering issues, as expected, for all of us."

The Thomas Matusiewicz, 68, was killed in Monday's attack. He never was charged with a crime in connection with the 2007 kidnapping although police did interview him.

His wife, Lenore, ultimately pleaded guilty and was sentenced to 18 months in prison on charges related to the abduction she carried out with their son.

After the children were returned to Belford, she sought to keep her former in-laws away from the girls. She told The News Journal that she feared for their safety if a Matusiewicz relative transported the girls.

"Relatives didn't cooperate in recovering the girls," Belford said after David Matusiewicz filed for joint custody and visitation from prison in 2010. "If we're talking about the grandfather, people should remember his wife pleaded guilty."

David Matusiewicz and his mother had left with the girls in an $80,000 motor home after telling Belford they were taking the kids to Florida for a vacation at DisneyWorld.

A former neighbor of Thomas and Lenore Matusiewicz was "not surprised" to learn Thomas Matusiewicz was involved in an attack on Belford, describing the elder Matusiewicz as "antsy" and increasingly upset over his son's family troubles.

"Once that stuff seemed to start happening, he wasn't shy about accusing his daughter(-in-law), talking about drugs and saying all kinds of things, like 'She shouldn't have the kids' and, 'They're no good,' " said Walter Rieth, who lived next to the ranch-style home here where the Matusziewiczes used to live.

"He wasn't happy about it. That's for darn sure," Rieth said. "He wasn't getting violent about it, but his voice would be raised, saying, 'They're no good for the kids. They need to leave them with my son.' "

Investigators say the elder Matusziewiczes moved to Edcouch, Texas, about 300 miles south of the federal penitentiary where their son had been housed.

Rieth was aware that Thomas Matusiewicz owned firearms, saying that his one-time neighbor talked about hunting while living on a farm in New Jersey before coming to Delaware.

"Tom was a nice enough fellow, but he was a little bit different," Rieth said. "He was kind of antsy. He'd talk, and it was like his mind seemed to be jumping around. ... I do know that he owned a number of firearms. I'd seen a number of things, but I didn't see him doing anything weird with weapons."

The Rieths said they had been living in suburban Smyrna, Del., for about a decade when the Matusiewicz family moved into the neighboring home a few years later.

"They pretty much kept to themselves," Roslyn Rieth said. "They were an older couple. At one point, we didn't see the wife anymore, and then we found out that the wife had left with the son and the children, and they wound up in South America and then came back up here. Afterward, we didn't hear about them, and the house went up for sale."

Thomas and Lenore Matusiewicz filed for bankruptcy in Hidalgo County, Texas, where Edcouch is located, in 2011. In their bankruptcy petition, they claimed to own at least one 9 mm pistol and 100 rounds of ammunition.

Two years ago, Lenore Matusiewicz wrote to Delaware Attorney General Beau Biden from Edcouch, urging him to re-examine the case and again claiming that Belford had abused her granddaughters.

"David is paying the price for trying to protect his children," Lenore Matusiewicz wrote.